In the season two episode 'Innocence' (where Buffy defeats the judge with a rocket launcher) there is one BIG mistake. Zander says to Cordelia in the library 'Meet at my house in half an hour' (or words similar). The next scene is in the morning, with Buffy storming into the school and questioning Ms. Calendar. THEN, it goes to a scene with Zander and Cordelia stealing the rocket launcher! It's night time and from the past! I don't want to sound nit-picky, but come on! How could this get missed?!

The scenes are not in order time-wise.
The first scene, let's say it's a Monday night at 8PM.
The next scene with Buffy, you see Buffy going to bed Monday and waking up Tuesday morning.
The scene after that with Xander (not Zander) and the gang is that same Monday night, only 30 minutes or so later.
For the plot and storyline of the episode, it clearly made more sense for them to air it in that order.